Van Os came to the world in Indonesia, on June 1, 1931. During his medical studies he worked at the Dutch Cancer Institute of Rijks University at Utrecht, Amsterdam, successfully completing his medical exams in 1959.
In his doctoral work he already concerned himself with ‘The Development and Evaluation of Multiload IUDs'. He completed his MD in Gynecology in 1965. Van Os led the Department of Gynaecology and Obstetrics in a cluster with the Free University of Amsterdam, subsequently working in the same department as senior consultant until 1992.
Van Os served and continues to serve in various functions for a number of international organizations (International Health Foundation, United Nations Fund for Population Activities, Society for the Advancement of Contraception); he is consultant to the Indonesian Family Planning Organization BKKBN and was Chief Editor for the specialized medical journals 'Advances in Contraception' (1985-1995) and 'Contraceptive Delivery Systems'.
His most important collaborations with pharmaceutical concerns involved Multilan, Switzerland (Medical Director 1974-1995), Akzo Pharma (1978-1990), Mona Lisa N.V. Homesteel (since 1990), Eurem Pharm (since 1994).
He penned more than 100 medical papers and lectures plus two textbooks about IUD's.
Van Os holds the patents and licenses for Multiload IUD Cu 250, Ml. Cu 375, Ml. Cu 375 short loop for China, Multiload Mark 2 plus Inserter, Multiload Cu 375 with Desogestrel release.
He was honored with the Gregory Pincus prize in 1979 and is an honorary member of Mother and Child Care at the University of Calcutta since 1987.
He has been chairman of Swing Group since 1991.